System for controlling medical imaging equipment motion

ABSTRACT

A system including a user input device for controlling a position of medical equipment is described. In an example embodiment, the user input device is configured to be coupled to the medical equipment and is responsive to an operator input representation of a desired movement of the equipment. A processor determines a direction in which the operator desires the equipment to move based on a device output.

This application is a divisional of U.S. application Ser. No.09/973,588, filed Oct. 9, 2001, which is hereby incorporated byreference. Now U.S. Pat. No. 6,785,578

BACKGROUND OF THE INVENTION

This invention relates generally to medical imaging, and moreparticularly, to positioning imaging components around a patient.

Diagnostic medical imaging requires accurate positioning of imagingequipment around a patient. Depending on the size and complexity of theequipment, the equipment can be positioned manually (e.g. dental X-rays)or through motorization of the equipment. With manual positioning, theoperator has full control over the device being positioned and isrestricted only by the range of motion of the equipment. Moreover,manually moving equipment is intuitive since one merely pushes and pullsthe equipment into the desired location.

Some imaging equipment is motorized in order to help the operator moveheavier equipment, or to facilitate advanced procedures in which theequipment must be precisely positioned or moved during an imagingprocedure. The user device for control of larger motorized equipmenttypically is a joystick or a force input device (e.g. a spring-loadedhandle with 1 to 3 degrees of freedom that measures the force applied tothe handle). The joystick or force input devices are often locatedremotely from the equipment (e.g. on a user control panel) and have noparticular relationship to the geometry of the machine. For example,left-right motion of the joystick may result in something other thanleft-right motion of the machine. Force input devices are sometimesattached directly to the device being controlled, and a force applied tothe input device results in machine motion in the same direction as theapplied force and a magnitude commensurate with the applied force.

In screening applications (e.g. mammography), there is a high-throughputof patients per day. Minimizing the time required for a particular exam,thus maximizing equipment and operator productivity, is highlydesirable. In interventional applications (e.g. vascular X-ray), focusedattention is on the patient and the medical procedure, and the controlof the imaging device should be as intuitive, effortless, and efficientas possible.

BRIEF SUMMARY OF THE INVENTION

In one aspect, a system for controlling the position of medicalequipment is provided. The system, in an example embodiment, comprisesat least one sensor configured to be coupled to the medical equipmentand responsive to an operator input representation of a desired movementof the equipment, and a processor coupled to the sensor for determininga direction in which the operator desires the equipment to move based ona sensor output.

In another aspect, a sensor comprising a core having an outer surfaceand a plurality of sensing areas on the outer surface is provided. Eachsensing area is responsive to operator input for generating a signalrepresentative of the operator input.

In yet another aspect, a medical imaging system is provided. In anexample embodiment, the system comprises a source for transmittingsignals towards a patient, a detector for detecting signals that havebeen transmitted through the patient, a movable member on which at leastone of the source and the detector are mounted, and a user input devicefor controlling a position of the movable members. The user input devicecomprises a plurality of sensors coupled to the movable members andresponsive to an operator input representation of a desired movement ofthe equipment. The system further comprises a processor coupled to theuser input device for determining a direction in which the operatordesires the member to move based on sensor outputs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an X-ray imaging system.

FIG. 2 is a schematic illustration of hand motion and device motion.

FIG. 3 is a schematic illustration of hand motion and intended devicemotion with an obstacle.

FIG. 4 is a schematic illustration of hand motion and compensated devicemotion with an obstacle.

FIG. 5 is a vector illustration of movement.

FIG. 6 illustrates one example segment in an 8-segment sensorarrangement.

FIG. 7 is a graph illustrating a nominal finite element analysis for the8-segment sensor arrangement.

FIG. 8 is a schematic illustration of an 8-segment sensor arrangementcontrol circuit.

FIG. 9 illustrates a capacitance based matrix touch switch.

FIG. 10 illustrates a sample segment of the switch shown in FIG. 9.

FIG. 11 is an exploded view of a segment of the switch shown in FIG. 10.

FIG. 12 is a schematic illustration of a 32-segment sensor arrangementcontrol circuit.

DETAILED DESCRIPTION OF THE INVENTION

The systems and methods described below are directed to operator controlof medical imaging equipment position. Generally, multiple proximitysensors are located on the machine to be controlled. The outputs of thesensors are processed using a vectorial addition method to determine howthe machine should move in response to an operator input. Moreover, inaddition to detecting and processing operator inputs, the proximity offoreign objects (e.g. auxiliary equipment, the patient) is detected.Therefore, the equipment can be moved in a manner that attempts tosatisfy the operator input as well as avoids collisions with surroundingobjects.

The systems and methods described herein are based on capacitancesensors. Other non-contact proximity sensors, such as infrared orultrasonic sensors, can be used. Capacitance sensors, however, have asimple construction and output, are not expensive, and facilitate easycustomization of sensing zones by merely positioning conducting surfaces(e.g. a conductive material such as copper foil) to define the zones.Further, the systems and methods can also be used in contact basedapplications.

The systems and methods described herein can be used in connection withmany different types of medical imaging systems. By way of example, setforth below is a description of one type of X-ray imaging system 10,illustrated in FIG. 1. Again, system 10 is described herein as anexample only, and the systems and methods described herein can be usedin connection with many different types of medical imaging systems,e.g., X-ray, computed tomography, magnetic resonance, positron emissiontomography, and ultrasound.

More specifically, and referring to FIG. 1, imaging system 10 is shownas including a base 14 and a positioning arm 16. Base 14 extends from aportable platform 18 having a plurality of wheels 20 so that base 14 ismovable relative to an object or patient 50 to be imaged. Rather thanwheels 20, other position altering devices can be employed. For example,a pivot can be provided to allow tilting and rotating arm 16 of theimaging equipment.

Arm 16 includes a first end portion 22 and a second end portion 24. Morespecifically, arm 16 rotates relative to base 14 about an axis ofrotation and moves relative to base 14 to alter the respective distancesbetween arm first end portion 22 and base 14 and arm second end portion24 and base 14.

An x-ray source assembly 26 is movably coupled to arm first end portion22. X-ray source assembly 26 includes an X-ray source 28 configured toemit x-ray signals. A detector assembly 30 is movably coupled to armsecond end portion 24. Detector assembly 30 includes a detector 32configured to receive the x-ray signals from said source 28 to generatean image of the object. Detector 32 can be moved up and down using amotorized control.

By moving arm 16 relative to base 14, the position of source assembly 26may be altered so that source assembly 26 is moved toward or away frombase 14. Altering the position of source assembly 26, alters theposition of detector assembly 30 relative to base 14 in an oppositedirection. The orientation of assembly 26 and assembly 30 to the patientaffects the image generated.

Detector 32, in one embodiment, is formed by a plurality of detectorelements 34 which together sense projected x-rays that pass through anobject. In the example embodiment, detector 32 is a flat panel, an imageintensifier, or film. In one embodiment, detector 32 is a solid statedetector or radiation imager comprising a large flat panel imagingdevice having a plurality of pixels 34 arranged in rows and columns.Again, the systems and methods described herein are not limited to usewith any one particular type of detector.

System 10 also includes a table 46 for supporting patient 50. Togenerate an image of patient 50, arm 16 is rotated so that sourceassembly 26 and detector assembly 30 rotate about patient 50. Morespecifically, arm 16 is rotatably coupled to base 14 so that detector 32and source 28 are rotated about object 50.

Movement of arm 16 and the operation of x-ray source assembly 26 anddetector assembly 30 are governed by a control mechanism 52 of system10. Controller, or control mechanism, 52 includes an x-ray controller 54that provides power and timing signals to x-ray source 28 and a motorcontroller 56 that controls the position of arm 16, source assembly 26and detector assembly 30.

In the example embodiment, a data acquisition system (DAS) 58 in controlmechanism 52 samples data from detector 32 for subsequent processing. Animage processor/reconstructor 60 (the term reconstructor as used hereinincludes reconstructors as are known in the computed tomography art, aswell as processors for processing data collected in a scan (i.e., notlimited to computed tomography image reconstructors)) receives sampledx-ray data from DAS 58 and performs high speed imageprocessing/reconstruction. The resultant image is applied as an input toa computer 62 which stores the image in a mass storage device 63.

Computer 62 also receives commands and scanning parameters from anoperator via a console 64 that has a keyboard. One or several associateddisplays 66 allows the operator to observe the resultant image and otherdata from computer 62. The operator supplied commands and parameters areused by computer 62 to provide control signals and information to DAS58, x-ray controller 54 and motor controller 56. Computer 62 operates atable motor controller 68 which controls position of motorized table 46relative to system 10.

In one embodiment, the user input device comprises multiple capacitancesensors located on base 14, source assembly 26, detector 32, positioningarm 16, and table 46. Each sensor yields information about the proximityof the operator (e.g. operator's hand) and other objects (e.g. patientbody) relative to the sensor. The information from each sensor isprocessed (e.g., by computer 62) using a vector addition algorithm, asdescribed below.

More specifically, the general principles of the vector additionalgorithm are described below with respect to FIGS. 2, 3, and 4.Referring to FIG. 2, there are no external obstacles illustrated, andthe objective is to move a device 80 as an operator's hand 82 approachesdevice 80. Device 80 moves directly away from operator's hand 82. Thecloser hand 82 is to device 80, the faster device 80 moves away fromhand 82. The operation becomes slightly more complicated as thepotential for external objects, or the control of multiple operators,becomes possible. These more complicated cases are illustrated in FIGS.3 and 4.

In FIG. 3, the operator is requesting that device 80 move away from hand82, yet move directly into an obstacle 84. The system should respond bymoving away from hand 82, and then slowing down as device 80 approachesobstacle 84. Eventually, device 80 should find an equilibrium positionbetween hand 82 and obstacle 84 without directly contacting either hand82 or obstacle 84.

FIG. 4 illustrates a case in which there is a trajectory along whichdevice 80 can move while satisfying the operators request to “move left”while simultaneously avoiding obstacle 84. In order accomplish thefunctionality illustrated in FIGS. 3 and 4, both the location andproximity of various objects along the device periphery should be known.

Although the illustrations in FIGS. 2, 3, and 4 appear two-dimensional,the principles can be easily generalized to three-dimensionalapplications depending on the functionality of the system to becontrolled.

FIG. 5 is a vector representation of accomplishing the movementillustrated in FIG. 4. Specifically, the output of each proximity sensoris used to calculate the speed and direction of a move given theproximity of objects. The direction of the move for a particular sensoris based on the orientation of that sensor and it is assumed that thesensor output is a scalar quantity (e.g. a voltage or single integer).Multiple sensors are attached to the device to provide the desiredspatial resolution and coverage of the device. The output from eachsensor, which consists of a signal strength (representative of speed)and a direction based on the orientation of each sensor, is then addedvectorially to create a composite move vector. This composite movevector accounts for surrounding objects. Such vector addition isimplemented in software, firmware or dedicated hardware. The device isthen commanded to move with the speed and direction of this compositemove vector. For example, the vectors which control movement of theparticular device are controlled so that the movement is consistent withthe composite move vector.

Set forth below are descriptions of two embodiments of capacitancesensor arrangements, sometimes referred to herein as user input devices.One embodiment is referred to as an “8-segment” sensor arrangement, andthe other embodiment is referred to as a “32-segment” sensorarrangement. Both embodiments are two-dimensional and sense objectproximity in a single plane. More particularly, the 8-segment sensorarrangement detects object proximity, while the 32-segment sensorarrangement detects “touch”. Therefore, while the 8-segment sensorarrangement uses the vector addition algorithm previously described, the32-segment sensor arrangement assumes that vectors have a length ofeither 0 or 1 depending on whether a particular sensor is touched (1) ornot touched (0). The sensors are configured to couple to medicalequipment. As used in this context, the “configured to couple” meansattached to, directly or indirectly.

Referring to FIG. 6, and regarding an 8 segment sensor arrangement 100,a portion of a core which comprises a circular plastic (e.g., an ABSplastic) ring 102 with a nominal outside diameter of 32 cm isillustrated. Alternatively, the core could be rectangular. The circularshape is the same size as the exterior of the 20 cm X-ray imageintensifier used on vascular X-ray imaging products commerciallyavailable from GE Medical Systems. Milwaukee, Wis., of General ElectricCompany. Eight sensor segments 100 are secured to an exterior surface106 of ring 102, with each sensor 104 covering a nominally 45° segment.Each 45° segment is divided into a primary sensing area 108, and aperiphery 110 of each segment is covered with a ground plane. The groundplane minimizes cross-segment sensitivity and electrical cross talkbetween segments. The ground plane also localizes the sensing area, sothose objects outside the desired sensing area are not detected. Thematerial shown in FIG. 6 is a thin copper foil bonded to the ring.Example dimensions are: A=5.13 inches, B=2.6 inches, C=0.36 inches, andD=0.125 inches.

In the example embodiment, the sizes of each segment and ground planeswere chosen based on a nominal finite element analysis shown in FIG. 7.The sensor has a sensitive area between 3 and 5 cm away from theexterior surface.

Each sensing area is connected to capacitive sensor electronics as shownin FIG. 8. The sensor arrangements include capacitive units 112 which,in one embodiment, are model QT9701B-S sensor units commerciallyavailable from Quantum Research Group, United Kingdom. Each sensor unit112 is coupled, via an 8 channel serial interface 114 with an RS232communications link, to a processor, illustrated as a personal computer(PC) 116. Of course, other communication links can be used. Theprocessor need not be a PC, however, and can be any device capable ofperforming the processing functions described below. The QT9701B-Ssensor unit also contains approximately 20 configurable parameters,which can be configured over the serial communications link. Thesoftware configuration interface ensures that all eight QT9701B-S sensorunits are configured identically so that the sensor sensitivity isuniform around the sensor periphery. In some applications, a non-uniformsensitivity may be desired, and either sensor units 112 can beconfigured differently, or the signal from each sensor unit 112 onprocessor 116 can be interpreted differently.

In FIG. 8, a software interface 118 for displaying configurationinformation on personal computer 116 also is illustrated. Rather thanactually connecting 8-segment sensor 100 to imaging equipment, the speedand direction of move information is computed using the vector additionalgorithm. An arrow displayed on a PC display 120 then indicates thedirection of the computed move. The speed of the computed move isrepresented by the size of the arrow, with a larger arrow representing ahigher speed. Thus, information about both the direction and speed thatthe imaging equipment would move in response to people and objects isdisplayed, while not requiring the complete imaging system.

Sensor units 112 operate autonomously, with no synchronization betweenthe sensor excitation/readout. Of course, for a synchronizedimplementation, integrated electronics would facilitate synchronizationbetween the excitation and measurement of each sensing segment, andtherefore further reduce cross-channel interference and sensitivity.

Regarding the 32-segment sensor arrangement, like the 8-segmentembodiment described above, a ring with a nominal outside diameter of 32cm is utilized. In the example embodiment, the capacitive sensor unitsused are model QT60320 sensor units, commercially available from QuantumResearch Group, United Kingdom. These sensor units are generally knownas capacitance based matrix touch switches.

The QT60320 sensor unit detects the capacitive coupling ofelectromagnetic fields. The matrix switch can be envisioned as 4 rowsand 8 columns of “wires”. The intersection of a particular row with aparticular column is a “switch”, though electrically there is no trueintersection of the rows with the columns. Each of these wires isexcited by the electronics and creates an electromagnetic field. When afinger, hand, or other object is placed in close proximity of anyintersection, the electromagnetic field of the corresponding row andcorresponding column are coupled, and this particular “switch” is turnedON. The output of the sensor at any given time is the state of all ofthe 32 switches formed by the intersection of the 4 rows and 8 columns.Unlike some “touch switches”, the QT60320 sensor does not requirepassing electrical “leakage” currents through the object being detected.Thus, the conductive wire or foil matrix can be completely enclosedbehind glass, plastic, or other material that is not electricallyconductive. A true “touch”, meaning direct contact to the conductivecomponents, is not required. The switch is known as a touch switchbecause close proximity is required, and for practical purposes this maybe indistinguishable from a touch, though electrically this non-contacttechnique has safety (e.g. freedom from electrical leakage currents) andreliability advantages (e.g. immunity to electrostatic discharge).

Referring to FIG. 9, a sensor 200 includes a conductive matrix 202arranged around the periphery of a 32 cm diameter core, illustrated as aplastic ring 204. The 4 “rows” correspond to 4 circular segments, eachcovering a nominally 90° arc and denoted by “X”, as shown in FIG. 10,which illustrates an “X” segment (covers 90°). Example dimensions are:E=27.52 cm, F=5 mm, G=8 cm, H=2 mm, I=3.3 cm, J=5 mm, and K=0.5 mm.

Referring to FIG. 11, within each 90° arc, there are eight smallersegments each covering a nominally 11.25° arc and labeled as “Y”.Example dimensions are: L=3.3 cm, M=2 mm, N=3 mm, O=1.5 mm, P=1 mm, Q=5mm, R=1 mm, S=2.5 mm, T=2.5 mm, U=1 mm, V=5 mm, and W=1.5 mm.

Each Y segment has a serpentine shape that is intertwined among“fingers” from the X segment. When an object such as a hand or finger(labeled FINGER in FIG. 11) comes into close proximity with the sensorsurface, the object typically covers several of the X “fingers”, andthus couples the electromagnetic fields of the corresponding X and Ysegments. This coupling of electromagnetic fields closes, or turns ON,the switch associated with the intersection of the corresponding X and Ysegments.

FIG. 12 is a schematic illustration of a sensing circuit arrangement for32-segment sensor 200. Sensor 200 is coupled to a matrix switch 206,which in the example embodiment is the QT 60320 switch commerciallyavailable from Quantum Research Group, United Kingdom. Switch 206 iscoupled to a processor illustrated as a personal computer (PC) 208 via aserial (RS232) interface board 210. Of course, other communication linkscan be used. The processor need not be a PC, however, and can be anydevice capable of performing the processing function described herein inconnection with the PC. Personal computer 208 configures and calibratesswitches 206. Nominally, each switch is identically configured toprovide uniform sensitivity. However, different switches may beconfigured differently depending on the particulars of the application,or to account for variability in different “switches” if the geometry ofthe “switches” is different. The output of sensor 200 is the discretestatus (i.e. ON or OFF) of each of the 32 switches. This information isread approximately every 50 ms and processed by personal computer 208.The ON/OFF information from each switch is processed on the personalcomputer using the vector addition algorithm described above. Switchstatus is displayed on a display 212 of computer 208.

Unlike the 8-segment prototype, the 32 segment arrangement does notprovide distance information about surrounding objects. Thus the vectoraddition algorithm involves adding the angles of those “switches” whichare on, and computing the direction of the move based on this angularinformation. The speed of the move is some nominal value appropriatelychosen for the equipment being controlled.

In FIG. 12, a display 212 of the move direction as computed by thevector addition algorithm is shown. Such display 212, of course need notbe present. The direction of the motion would be in the direction asindicated by the arrow.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A sensor comprising a core having an outer surface, a plurality ofsensing areas on said outer surface, each said sensing area responsiveto at least one object within a sensory field of said sensor, whereinthe at least one object comprises at least one of an operator inputrepresentative of a desired movement of said movable member and anobstacle in proximity with said movable member.
 2. A sensor according toclaim 1 wherein said core comprises plastic, and wherein each of saidsensing areas comprises a conductive foil bonded to said plastic.
 3. Asensor according to claim 1 wherein said core has one of a circular andrectangular cross sectional shape.
 4. A sensor according to claim 1wherein a ground plane is at a periphery of each sensing area.
 5. Asensor according to claim 1 wherein the operator input is based on aposition of an operator's hand.
 6. A sensor according to claim 1 furthercomprising eight sensing areas, each of said sensing areas comprising aconductive foil, and ground planes at a periphery of each said sensingarea.
 7. A sensor according to claim 1 further comprising thirty twosensing areas, each sensing area coupled to a matrix switch.
 8. A sensoraccording to claim 1 wherein said sensors comprise at least one of acapacitance sensor, an infrared sensor, and an ultrasonic sensor.
 9. Asensor according to claim 1 wherein said sensor determines both a speedand a direction in which the equipment is to be moved.
 10. A sensoraccording to claim 1 wherein at least some of said sensors comprisecapacitance sensors, each of said capacitance sensors being one of aproximity sensor and a touch based sensor.
 11. A sensor according toclaim 1 wherein said sensor is responsive to a position and speed of anoperator's hand with respect to said sensor.